Step switch servo drive system



y 21, 1964 1. 1... MARIN 3,142,010

STEP SWITCH SERVO DRIVE SYSTEM Filed Aug. 3, 1962 2 Sheets-Sheet 1 Fol/ 50 Zeaaf;

Z/ pie fish JCZnIFa/ Z2 if As! 5 77,0; JAZZ/32% INVENTOR. [er/A ,6. Mme/N M 7 Wh z ATTORNEY 2 Sheets-Sheet 2 July 21, 1964 L. MARIN STEP SWITCH SERVO DRIVE SYSTEM Filed Aug. 5, 1962 fey 4;: A WAR/N Qur) Ldmam i ATTORNEY United States Patent 3,142,010 STEP SWITCH SERVO DRIVE SYSTEM Irving L. Marin, De Witt, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Aug. 3, 1962, Ser. No. 214,773 16 Claims. (Cl. 318-30) The present invention relates to remotely controlled switching devices and more particularly to a rotary switch having a discrete number of steps or positions at which positive contact must be made to one of these positions irrespective of the intermediate position of a remote controller.

Ordinarily a dual speed servo control system consists of high and low speed control transformers which act to eliminate errors arising therebetween. As presently used these systems provide, at a relatively high cost, a certain degree of accuracy between the transmitter shaft and the driven shaft. This, however, is not applicable to a switch which has discrete stops since in the majority of cases, transmitter shaft would not be aligned with any particular switch step and even if it were possible to adapt this system to such a switch the inherent hesitation in the system selecting the nearest corresponding step would make it undesirable. The inability to employ the standard two-speed servo system is inherently limited by the delay and inability of the system in making a positive selection although several proposals in this respect have been suggested but without apparent success. The problem simply stated involves the use of a continuous synchro transmitter which must operate and control a terminal or load and be capable of converting this continuous input into an output at the load that can only be stopped at single discrete positions and not in between.

In view of the foregoing it is an object of this invention to provide an efficient, inexpensive and simple servo system capable of operating a terminal device such as a rotary step switch having only discrete stops, from a continuous input signal, with the further attendant ability to select accurately, the nearest discrete step of switch to the input without hesitation or relay.

Other objects and advantages will appear from the following description of an example of the invention, and the novel features will be particularly pointed out in the appended claims.

In the accompanying drawings:

FIG. 1 is a block diagram of one embodiment made in accordance with this invention, and

FIG. 2 is the wiring schematic of the block diagram representation of FIG. 1.

In the illustrated embodiment of FIG. 1, an indicator or a servo motor is oriented for a particular angle which by way of example may be the bearing on which it is desired to train or beam a sonar signal. This indicator is mounted so as to rotate therewith a shaft 11 and as it assumes a new position it also reorients the synchro transmitter 12 in alignment therewith. It is also possible to manually turn the transmitter directly and thereby eliminate the necessity of indicator 10 or shaft 11 but in order to provide a more complete disclosure these elements have been retained. The output or stators of the transmitter are connected to a synchro control transformer whose speed is the same as that of the transmitter 12. The control transformer 13 is carried by a drive shaft 14 and rotates therewith. The shaft 14 also carries for rotation with it a multi-position rotary step switch 15, a high speed synchro control transformer 16 and a tachometer 17. The frame of the rotary switch may rotate with the shaft while its contact arm or arms are held stationary or as is usual the contact arm turns in response to and with the shaft. Cable 18 contains a number of wires which are connected to the switch terminals and this cable is connected with its wires to the equipment (not shown) to be controlled by the switch. The multiple or high speed transformer is coupled to the drive shaft, as by either internal or external gears, so that it rotates N times for every single revolution of the shaft where N is the ratio of speeds between this transformer and control transformer 13 and is also the number of discrete positions which load switch 15 may assume. Motor 19 is likewise attached to the drive shaft 14 for motivating or turning it depending on its input signal.

The output or error signal of the low speed trans former 13 is coupled to an error discriminator 20 which will generate therefrom an output only when the input exceeds a certain predetermined input signal level. The discriminator output is made to activate a switch control device 21 which, when activated, connects the low speed transformer output directly to the motor via a servo amplifier 22. In the other contact state of device 21, the high speed transformer output is coupled to the motor via the amplifier 22 so that one transformer or the other is feeding an error signal to the motor. There is, therefore, in effect an error feedback loop network with the addition thereto of the tachometer output voltage.

Detailed operation and circuitry are illustrated in FIG. 2 wherein the indicator 10 may assume the form of a switch or any continuously rotatable device and is directly coupled, as is synchro transmitter 12, to a rotatable shaft 11. The rotor voltage for the generator or transmitter is supplied from an external source (not shown) and is of the proper value and frequency, as for example, v., 60 cycles for the most common synchros. This voltage is applied to the rotor leads 23 while the stator leads 24 are connected to the appropriate stators leads 25 of synchro control transformer 13. The transmitter and transformer 13 are chosen to be of the same operating speed namely one revolution of each produces a full cycle of output voltage and they are operationally compatible. This transformer as well as tachometer 17, rotary switch 15 and the high speed control transformer 16 are all mounted for unitary rotation with drive shaft 14 except that the high speed transformer is coupled to rotate so that for a complete revolution of the drive shaft the transformer will make the same number of revolutions as there are discrete switch steps. Merely for illustrative purposes, let us assume that the rotary switch 15 has 72 positions then the high speed transformer should be a 72 speed device while the low speed transformer and the generator must be single or one speed synchros. Under these conditions, the switch contacts would be spaced approximately 5 degrees apart and for every complete turn of the drive shaft the 72 speed transformer would make 72 revolutions. In other words, for every 5 degrees of switch turn the 72 transformer makes a complete rotation and a complete cycle of voltage output. This 72 transformer has its rotor leads connected to a source of voltage proper for Zero order operation.

Servo drive motor 19 rotates the drive shaft 14 in accordance to the signal fed to it by the servo amplifier 22 and the control signal to the amplifier is derived from either of the two transformers dependent on the activity of the error discriminator 2d. The output of the one speed transformer is terminated across a voltage divider network comprising resistors 26 and 27. A portion of the output is picked-off between these resistors and connected to contact 28 of relay switch 29 and the full output is connected to the other contact 30. In a like manner, that portion of the output of the 72 transformer developed between divider resistors 31 and 32 is applied to contact 33 of relay switch 34 while the other contact 35 of this switch receives the full one speed transformer output. The movable or controlled arm 36 of switch 34 is connected to the servo amplifier input while the arm 37 of switch 29 is connected to one side of the parallel combination of capacitor 38 and resistor which in turn are tied to one rid 45 of vacuum tube 41. This tube 41 may be either a dual triode or two separate triodes. The output of these tubes is applied to the coil 42 of relay switch circuit 21 and the current passing therethrough causes the movable arms 37, 36 and 43 of switches 29, 34 and 44 to be pulled into their activated position as shown in this figure.

Considering for the moment the relay in its Clo-energized state a portion of the one speed transformer output determined by the ratio of resistors 25 and 27, is applied through contact 28, arm 37 and the parallel combination 38 and 39 to the grid 45) of tube 41!. This A.C. synchro voltage is rectified and capacitor 35 is caused to charge egatively thereby reducing the grid voltage. With this action the tube current is reduced and the plate voltage increased. The grid voltage at tube 45 also rises by way of the plate voltage being coupled through resistor 46 to grid 47 thus causing increased plate current in tube 45. B+ and B voltages are supplied to the tubes through resistor 48 and variable resistor 49. Variable resistor 49 is adjusted so that when the divided error output of transformer 13 exceeds some predetermined value (voltage corresponding to an error voltage in excess of 3 degrees) the current through coil 42 is sufiicient to energize and activate the arms of the switches. Capacitor Stl across the coil smoothes the output and reduces relay chatter.

When the relay is energized, the fully error output of the one speed transformer is applied through contact 35 and arm 36 to the servo amplifier and by arm 3'7 and contact 30 to the grid dtl. This error voltage at the amplifier causes the servo motor 19 to rotate shaft M to reduce the error voltage and to align shafts l1 and M. This error is reduced until it corresponds to a voltage equal to one degree and then the relay becomes de-energized. Accomplishment of this is easily attained by adjustintg the ratio of resistors 25 and 27 and the setting of resistor 49. In other words, the relay picks up at errors exceeding three degrees and drops out when the error is less than one degree. The sequence of events is as follows: When the one speed error exceeds three degrees, the plate current of tube 45 is suflicient to cause the relay to pick-up and apply the full error to the amplifier which in turn drives the motor in a direction to reduce this error. The relay drops out when the error becomes one degree and the 72 transformer error is applied by way of switch 34 to the amplifier and drives the motor to rotate the shaft 14 to properly position the arm of the rotary switch to the nearest step or five degree position.

With both transformers aligned for zero rotation, as an example, the transmitter is now turned to 23 degrees. This causes the one speed transformer to control the motor 19 until the shaft 14 is rotated to approximately 22 degrees and at the same time the shaft 14 has rotated the 72 transformer four times degrees equals 1 revolution) plus an additional two-fifths of a turn. At this time, the relay drops out and the 72 transformer error is applied to the amplifier and causes the motor to rotate the shaft back to its zero position. Since the zero position of the 72 transformer is made to correspond to a step in the rotary switch then this transformer will always cause shaft rotation to the nearest step. One complete revolution of this high speed transformer is made by its coupling to the drive shaft, to occur when the rotary switch passes between steps whereby the speed of the transformer is equal to the total number of steps of rotary switch and it can only assume a zero position at the nearest of these steps. The discriminator 2t) switches the input to the servo amplifier from the error voltage of the one speed transformer to that of the 72 transformer and there is no possibility of any indecision on the part of the entire device in selecting the correct rotary switch position in view of the fact that the repositioning of the shaft by the 72 transformer cannot cause an error in excess of three degrees (returns to zero by the shortest angle which always corresponds to less than 2.5 degrees).

In order to stabilize the high speed loop and its operation, the full tachometer voltage is applied to the servo amplifier through relay switch 44 when the relay is deenergized and the high speed transformer error is controlling the motor. Only a portion thereof is applied at all other times. It should further be noted that although particular speeds, and switch steps, etc., have been given these may assume any value as N and for each, the relay pick-up adjusted to a value just greater than 360/2N. As an example, it is desired to position a 36 step rotary switch to the nearest step, then a 36 and one speed transformer are used and the 36 speed transformer is coupled to the drive shaft to rotate 36 times for every single shaft rotation. In this case, since the steps are 10 degrees apart and there are 36 rotary steps the relay is adjusted to pick up at error voltages of the one speed transformer exceeding six degrees and drop out at approximately two degrees.

The operation herein described makes use of a two speed synchro system on the load and a single one speed generator for the input. The gear ratio between load synchro transformers is selected to be the same as the number of stops or rotary switch positions (e.g., 72, 36 etc.). The one speed transformer is connected in the normal fashion to the generator or director while the high speed (72, 36 etc.) transformer is connected to a fixed value of voltage (zero order signal). As the load shaft rotates five/ten, etc., degrees, the high speed transformer goes through a complete cycle of electrical (error) output. The error angle between the generator shaft and the load shaft is continuously monitored by or at the one speed transformer and when this corresponds to some value less than three degrees, six degrees, etc.,

the servo motor is caused to come under the control of the high speed transformer. When it exceeds this value the motor is controlled by the one speed transformer. The switching of control from the one to the high speed transformer and the reduction of its error to zero, positions the load shaft and rotary switch to the nearest acceptable stop position. Where the problem of backlash is present, the switching of control may be delayed some what as by causing the relay to energize as for the 72 position switch at values above three degrees and become de-energized at one degree so that both hesitation and sudden changes in rotation and direction are minimized.

It will be understood that various changes in the details, materials and arrangements of parts and steps, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. A device for converting any angular indication into the nearest corresponding one of a number N of equally spaced discrete angular positions which comprises a load shaft, a position transmitter displaced at some angular position, receiving means for said transmitter, electrical connections between said receiver and said transmitter, a position device having a speed N times that of said receiving means and electrically connected to produce an output voltage dependent on its angular displacement from a reference position, operative connec tion between said position device, said receiving means and said load shaft, motive means for driving said load shaft in response to an error voltage in a direction to minimize said error voltage, selector means for applying the error voltage generated by said receiving means according to the angular difference between the position of said load shaft and said some angular position to said motive means when said difference is just in excess of 360 degrees/2N and for applying the output error voltage generated by said position device thereto for smaller differences whereby when said reference position corresponds to Zero angular displacement of said load shaft and said shaft is turned by said motive means in the direction of said some angular position, said receiving means error voltage will decrease until it corresponds to approximately less than 360 degrees/2N whereupon said position device will supply to said motive means an output voltage to rotate said shaft to the nearest of said 360 degrees/N discrete angular positions corresponding to said some angular position.

2. The device according to claim 1 wherein said position transmitter is a synchro generator and said receiving means and said position device are synchro control transformers.

3. The device according to claim 2 wherein said m0 tive means is a servomotor coupled to said load shaft.

4. The device according to claim 3 wherein said selector means includes adjustable voltage discriminator means for supplying an output dependent on said error voltage.

5. A device for converting any angular indication into the nearest corresponding one of a number N of equally spaced discrete angular positions which comprises a load shaft, a synchro generator displaced at some angular position, a first synchro control transformer electrically connected to said transmitter for receiving angular information thereof and for producing an output error voltage dependent on its angular displacement relative to said some angular position, another synchro control transformer of a speed N times that of said first transformer and internally connected to produce a complete cycle of output voltages for every complete revolution thereof, said output being dependent on its angular displacement from a reference, means mounting said first synchro transformers for 1:1 rotation with said shaft, second means mounting said another transformer for N rotations thereof for every rotation of said shaft, a servo motor coupled to said load shaft for rotation thereof in response to the level of an input voltage thereto, adjustable voltage discriminator means for producing an output dependent on the input thereto, said error voltage of said first transformer coupled to said discriminator means, selector means activated by said output of said discriminator means for applying said first transformer error voltage to said motor dependent on said error voltage and for applying said output voltage of said another transformer to said servo motor at other times, whereby when the discrimination level of said means is adjusted to the error so that voltage of said first transformer will be applied to said motor until said error voltage is decreased by the action of said motor in reducing the angular displacement error of said shaft relative to some angular position to that equivalent to rotation of said another transformer of less than one and greater than one half revolution and then said another transformer voltage will activate said motor to position said load shaft to rotate said another transformer to the reference position whereby said shaft may only assume discrete angular positions corresponding to one complete revolution of said another transformer.

6. The device according to claim 5 wherein said selector means includes a relay coil having associated therewith and operable thereby movable contacts, said contacts being in ser'es between the output of said transformers and said motor whereby only the output from one of said transformers is connected to said motor at any one time.

7. The device according to claim 5 further including a servo amplifier connected between said selector means and said motor.

8. The device according to claim 6 further including an N position rotary switch carried by and having its movable contact rotatable with said load shaft.

9. A servo driven rotary step switch device for positioning an N step rotary switch to the nearest step thereof corresponding to some angular position which comprises: said rotary switch, a load shaft, a single speed synchro generator displaced at said some angular position, a single speed synchro control transformer electrically coupled to said transmitter and capable of producing at its output terminals an output error voltage dependent on its angular displacement from said some angular position, an N speed synchro control transformer having stator winding connections to produce a complete cycle of output voltage for every revolution thereof, said output voltage being dependent on its angular displacement from a reference position, means mounting said switch, said single speed transformer on and for direct rotation with said shaft, second means mounting said N speed transformer on said shaft for producing N rotations thereof for every rotation of said shaft, servo motor means including a servo amplifier, said motor coupled to said shaft for rotation thereof, selectably, adjustable voltage discriminator means having input and output terminals and capable of producing an output dependent on the input thereto, a relay coil having associated therewith sets of separate contacts movable in response to the current activity in said coil, said coil connected to said discriminator output terminals, one set of said contacts in series connection between said sevro motor means and said single speed transformer, another set of said contacts in series connection between said servo means and said N speed transformer for completing said connection only when the connection controlled by said one set is not completed, an operative connection between said single transformer output terminals and said discriminator input terminals, whereby said shaft will rotate said switch to the nearest step in response to the alternate control action of said transformers when said discriminator is selective ly adjusted to produce a movement in said contacts to shift the connection of said servo means from said single transformer to said N speed transformer after said single transformer error is less than A degrees where A degrees is equal to 360/ 2N 10. The device according to claim 9 further including a tachometer coupled for rotation with said shaft and having its output connected by still another set of said contacts to said servo means.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A DEVICE FOR CONVERTING ANY ANGULAR INDICATION INTO THE NEAREST CORRESPONDING ONE OF A NUMBER "N" OF EQUALLY SPACED DISCRETE ANGULAR POSITIONS WHICH COMPRISES A LOAD SHAFT, A POSITION TRANSMITTER DISPLACED AT SOME ANGULAR POSITION, RECEIVING MEANS FOR SAID TRANSMITTER, ELECTRICAL CONNECTIONS BETWEEN SAID RECEIVER AND SAID TRANSMITTER, A POSITION DEVICE HAVING A SPEED "N" TIMES THAT OF SAID RECEIVING MEANS AND ELECTRICALLY CONNECTED TO PRODUCE AN OUTPUT VOLTAGE DEPENDENT ON ITS ANGULAR DISPLACEMENT FROM A REFERENCE POSITION, OPERATIVE CONNECTION BETWEEN SAID POSITION DEVICE, SAID RECEIVING MEANS AND SAID LOAD SHAFT, MOTIVE MEANS FOR DRIVING SAID LOAD SHAFT IN RESPONSE TO AN ERROR VOLTAGE IN A DIRECTION TO MINIMIZE SAID ERROR VOLTAGE, SELECTOR MEANS FOR APPLYING THE ERROR VOLTAGE GENERATED BY SAID RECEIVING MEANS ACCORDING TO THE ANGULAR DIFFERENCE BETWEEN THE POSITION OF SAID LOAD SHAFT AND SAID SOME ANGULAR POSITION TO SAID MOTIVE MEANS WHEN SAID DIFFERENCE IS JUST IN EXCESS OF 360 DEGREES/2N AND FOR APPLYING THE OUTPUT ERROR VOLTAGE GENERATED BY SAID POSITION DEVICE THERETO FOR SMALLER DIFFERENCES WHEREBY WHEN SAID REFERENCE POSITION CORRESPONDS TO ZERO ANGULAR DISPLACEMENT OF SAID LOAD SHAFT AND SAID SHAFT IS TURNED BY SAID MOTIVE MEANS IN THE DIRECTION OF SAID SOME ANGULAR POSITION, SAID RECEIVING MEANS ERROR VOLTAGE WILL DECREASE UNTIL IT CORRESPONDS TO APPROXIMATELY LESS THAN 360 DEGREES/2N WHEREUPON SAID POSITION DEVICE WILL SUPPLY TO SAID MOTIVE MEANS AN OUTPUT VOLTAGE TO ROTATE SAID SHAFT TO THE NEAREST OF SAID 360 DEGREES/N DISCRETE ANGULAR POSITIONS CORRESPONDING TO SAID SOME ANGULAR POSITION. 